In PostgreSQL 10.1 I create the following table:
CREATE TABLE nationality_cumulative_criteria
id smallint NOT NULL,
country_set character varying(2) NOT NULL,
number smallint NOT NULL
I wish to add a constraint (exclude) which will not allow, for example, "US" to appear in different tuples but only in one.
I have already checked and found only cases with ranges and functions but not with arrays of character elements.